<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" :ref="item"
        @click="handleLetterClick" 
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"       
        >{{item}}</li>
    </ul>
</template>

<script>
export default {
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    computed:{
        letters () {
            const letters =[]
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data (){
        return {
            touchStatus :false,
            startY :0,
            timer:null
        }
    },
    updated (){
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick (e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart (){
            this.touchStatus = true
        },
        handleTouchMove (e){
           if(this.touchStatus){
               if(this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(()=>{                
               const touchY = e.touches[0].clientY -79
               const index = Math.floor((touchY-this.startY)/20)
               if (index >= 0 && index<this.letters.length) {
                    this.$emit('change',this.letters[index])
               }              
           },16)
           }
        },
        handleTouchEnd (){
            this.touchStatus = false
        }

    }
    
}
</script>

<style lang="stylus" scoped>
    @import '~styles/varibles.styl';
    .list
        position :absolute
        top: 1.58rem
        right :0
        bottom :0
        width :.4rem
        display :flex
        flex-direction :column
        justify-content :center
        .item
            text-align :center
            line-height :.4rem
            color :$bgColor
</style>
